Well adapted
Apple snails are exceptionally well adapted to tropical regions with periods
of drought alternated with periods of excessive rainfall. This adaptation is
reflected in their life
style: moderately amphibious and being equipped with a shell door enabling
the snail to close its shell
(to prevent drying out while hiding in the mud during dry periods).
A typical adaptation of apple snails is the combination of a branchial respiration
system comparable with the gills
of a fish (at the right side of the snail body) and a lung
(at the left side of the body).
This lung/gill combination expands the action radius of the snail in search
for food.
Many apple snail species deposit the eggs
above the waterline in a calcareous clutch. This remarkably strategy of these
aquatic snails protect their eggs against predation by fish and other water
inhabitants. Another predator specific adaptation
in the apple snail genera Pomacea and Pila,
is the tubular
siphon at their left side, used to breathe air while they stay submerged,
thus making them less vulnerable to snail eating
birds.
Apple snails inhabit various ecosystems: ponds, swamps and rivers. Although
they occasionally leave the water, they remain mainly submerged.
In spite the fact that many snail species are hermaphrodite (being male and
female at the same time) apple snails are definitely not: they have separated
sexes (gonochoristic) and a male
and a female are needed for reproduction.
For more info about the anatomy of apple snails: take a look at the anatomy
section of this site.

A common aquarium pet
The apple snails are popular aquarium-pets because of their attractive appearance
and size. When taken good care
of some apple snail species can reach a large size (15 cm / 6 inch diameter
in case of Pomacea maculata,
sometimes faulty referred to as Ampullarius gigas). Apple snails are
in fact the biggest living freshwater snails on earth. The most common apple
snail in aquarium shops is Pomacea diffusa
(spike-topped apple snail). This species
comes in different colours from brown to albino or yellow and even blue, with
or without banding. The
body of these snails also shows great variation from black to yellow and
grey. Another common apple snail is Pomaceacanaliculata,
this snail is bigger, rounder and is more likely to eat your plants, which makes
it less suitable for most aquaria. These snails also come in different shell
and body colours. The Giant ramshorn snail, Marisa cornuarietis, although
not always recognized as an apple snail due to its discoidal shape, also ranks
the popular aquatic pets.
Occasionally, the Florida apple snail (Pomacea
paludosa) is found in the aquarium trade and are often wild collected
from ditches and ponds in Florida. The giant Pomacea maculata,
raremy makes its way into aquaria. With tropical fish expeditions, sometimes
other apple snail species
are collected and offered for sale.
Apple snails are often sold under the name Golden mystery snail and are
given incorrect names like Ampullarius for the genus instead of Pomacea
and species names like gigas instead of maculata. More info about
this can be read in the species
section of this website.
For more info about how to keep and breed apple snails: take a look at
the care
section of this site.

A blessing or a pest?
In the 1980's, the genus Pomacea (like Pomacea
canaliculata)
was introduced in Taiwan to start an escargot industry. Such food culture
can provided protein for the local population, especially useful for the farmers,
who primary live on a rice diet, low in proteins. However, the snails didn't
become a culinary success. It also became quickly clear that the imported species
were able to transfer the Angiostrongylus
cantonensis (rat lungworm) parasite
just like the native apple snail population (Pila).
This parasite spends a part of its life cycle in apple snails and can infect
humans when the snail isn't cooked long enough before consumption.
Instead of becoming a food source they
escaped, and became a serious pest,
posing a real threat to the rice production
and the environment. During the 1980's the introduced snails rapidly
spread to Indonesia, Thailand, Cambodia, Hong Kong, southern China, Japan
and the Philippines and there are indications that they are currently invading
Australia. Nevertheless, apple snails are considered a delicacy in several regions
and they are often sold in Oriental markets for consumption.
In 1989 Pomacea canaliculata
was introduced in Hawaii to serve as a food
source and aquarium pet. Some snails escaped to the wild and turned into
a serious pest in the taro and rice fields. Although a few restaurants serve
them, the apple snail didn't become a great gastronomic success here either.
Recent research reveals the catastrophic nature of the Pomacea invasion
in new habitats: the snail herbivory drastically alters the state and function
of invaded natural wetlands. When the plants are consumed, nutrients in the
system are shunted to phytoplankton instead of the plants which creates dense
algal blooms (Carlsson et al in press. 2004). Pomacea and Marisa species have been introduced in Africa and
Asia to control snails(Planorbidae:
Bulinus sp. and Biophalaria sp.), which serves as intermediate host
for trematoda parasites. These parasites
can cause swimmers itch and schistosomiasis, a disease that affects over 200
million people in tropical regions. Despite the fact these tremadote parasites
do not complete their life cycle in apple snails, apple snails themselves can
carry these parasites and nematodes of the genus Angiostrongylus. Angiostrongylus
cantonensis can afflict humans and cause eosinophilic meningoenchephalitis.
One of the species was introduced as bio-agent is Marisa cornuarietis
. This apple snail competes with other snails and predates on them. Hopefully
Marisa is less likely to become a pest for the food production.

Update: In late July 2009 an incipient invasion by Pomacea
canaliculata was detected
in the Ebro Delta, on the Mediterranean shore of Catalonia, Spain. By early
September the spread of this applesnail was tremendous, with huge economic losses
to rice cultivation. Research on this population's biology and possible control
methods is ongoing. TV news on the topic: http://www.tv3.cat/videos/1478229/El-caragol-poma-envaeix-lEbre.

Conclusion: The recent spread of apple snails over the world and their
ability to become a pest illustrates the dangers
that come along the introduction of non-native species. It should be clear that
this is the main reason why many countries have very strict rules when it comes
to importing foreign animals like apple snails (and other animals).
"It should be clear: never release your apple snails in local ponds or rivers!"